This invention relates generally to the field of talc and more specifically relates to the use of a treated talc in paper products.
In the field of offset printing, the ink is first transferred from the printing plate to a blanket and then from the blanket to paper. This offset mode is also used commercially for printing letterpress, called dry offset, or gravure, called offset gravure. In offset printing, some picking of fibers or fillers from the paper surface, called linting or dusting, is normal due to some stiff, unfibrillated fibers that are not completely bonded to the sheet. Offset linting or dusting is a sheet surface phenomenon. However, these fibers and fillers because they are loosely bound to the paper can be transferred to the blanket, which will cause printing imperfections in resultant copies and inferior print copy. In addition, excessive linting or dusting will also lead to increased blanket maintenance. Thus, offset printers desire to use paper which does not lint or dust excessively.
In the paper-making process, cellulosic fibers are softened with water before being processed into paper. Fillers such as clay, titanium dioxide, talc, and calcium carbonate, are added to the papermaking process to improve paper properties such as opacity, brightness, and printability. Each filler is unique due to differences in physico-chemical and morphological properties. One example of a substance which will reduce linting or dusting is clay. Titanium dioxide is an excellent filler for opacity purposes due to is high refractive index and particle size. Due to its hydrophobicity, talc is an excellent pitch/stickie control. In addition, talc is an excellent filler for purposes of improving machine drainage, sheet smoothness and printability. However, as a filler, talc does not affiliate with the water-based cellulosic fibers as well as certain other fillers that are more hydrophilic. Thus, a method of modifying talc""s affinity to the cellulosic fibers of the raw paper is needed.
This invention discloses a sized and treated talc composition that is useful in preventing dusting or linting of paper when such talc is added to paper pulp during the paper making process. Also disclosed is a method of preparation of the talc of the present invention and its use in making paper. More particularly, the talc of the present invention is milled to have a particle size of less than 10 micrometers and a cationic charge to the surface of the talc particles. For example, a cationic charge can be added to the particle by mixing talc particles with water to create a slurry and, adding a cationic compound to the slurry. In preferred embodiments, the cationic compound is selected from cationic wet-end starch, cationic wax-based emulsion, polydadmacs and carboxymethylcellulose. Also, preferably, the talc particles have a top size of less than about 1.5% and a particle size of about 5 microns.
The present invention is also directed to a paper product which includes the talc composition of the present invention and a method for making such a paper product. The method includes adding the talc additive to a paper pulp and forming the paper pulp into a paper product.